Add #warning directive

[Headline]

Here's my test code along with compiler outputs. The first is how the current #error directive functions, and the second is the new #warning directive

/*
C:\Users\Micha\Desktop\New folder\sourcepawn\build\compiler\spcomp>spcomp test.sp
SourcePawn Compiler 1.10
Copyright (c) 1997-2006 ITB CompuPhase
Copyright (c) 2004-2017 AlliedModders LLC

test.sp(2) : fatal error 194: user error: testing 1 2 3


Compilation aborted.Code size:                0 bytes
Data size:                0 bytes
Stack/heap size:      16384 bytes
Total requirements:   16384 bytes

*/
#error testing 1 2 3 

int main()
{

}

/*
C:\Users\Micha\Desktop\New folder\sourcepawn\build\compiler\spcomp>spcomp test.sp
SourcePawn Compiler 1.10
Copyright (c) 1997-2006 ITB CompuPhase
Copyright (c) 2004-2017 AlliedModders LLC

test.sp(2) : warning 241: user warning: testing 1 2 3

Code size:               24 bytes
Data size:                0 bytes
Stack/heap size:      16384 bytes
Total requirements:   16408 bytes

1 Warning.
*/
#warning testing 1 2 3 

int main()
{

}

Fixes #169

[asherkin]

Mystery tabs.

[asherkin]

Can we use one of the unused ones?

[Headline]

I don't see why not, is it generally preferred to use the lowest unused spot?

[asherkin]

Ya, preferred, but isn't super important.

[KyleSanderson]

Patching holes is definitely a nice to have.

[Headline]

Will do. I’ll probably commit in the coming days

[Headline]

Alright. Let me know if there's anything else.

@dvander